[thomasgarrett455]

Fixes #95

Problem

On a fresh igniter install the config.exs would get default endpoints but, the router would get
"" as the :run and :validate endpoints, not the default "/rpc/*" endpoints

Root Cause

During the igniter install the new config values are only a pending edit. So, when add_rpc_routes/2 calls Application.get_env/2 it does not have the configured routes.
When no routes are set Application.get_env/2 defaults to nil. Hence, the empty routes in the router file.

The Fix

I added module attributes to the top of the install file to keep config.exs and router fallback in sync.
The 2 literals that were hardcoded in the install file were changed to the attributes. Inside the add_rpc_routes/2
function the defaults are now being passed into Application.get_env/3. These will be used only when
the key isn't already set from the user's configured endpoint.

Tests

Tests were added to ensure:

• A fresh install will produce the default endpoints,
• A user with a single endpoint configured will keep that endpoint and get the default endpoint for the other,
• A user with both endpoints already configured will keep them.
• A user with an already configured router file will not get duplicate endpoints.

Notes

Apps already installed with this bug won't be repaired because an empty route ("") that was added by a previous
install will still be counted as a route and therefore the installer will use it as an already configured route.

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• Features include unit/acceptance tests
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